Control apparatus for automatic transmission

ABSTRACT

In an apparatus for controlling an automatic transmission connected to a prime mover mounted on a vehicle, having a torque converter equipped with a lock-up clutch, when predetermined operating conditions of the vehicle are satisfied at drive-off, a lock-up clutch engaging circuit is formed through a hydraulic supply circuit. Next it is determined whether engage-position sticking malfunction of the lock-up clutch has occurred based on a ratio of an input rotational speed of the automatic transmission relative to an output rotational speed of the prime mover and a change rate of the output rotational speed of the prime mover when the lock-up clutch engaging circuit has been formed, and fail-safe control is then implement when the sticking is determined.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2014-145895 filed on Jul. 16, 2014, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a control apparatus for an automatictransmission, more specifically to a control apparatus for an automatictransmission that can reliably detect or determine malfunction of atorque converter lock-up clutch and implement appropriate fail-safecontrol when malfunction is determined.

Description of Related Art

A technique for detecting or determining lock-up clutch malfunction inan automatic transmission equipped with a torque converter having alock-up clutch, more precisely for detecting or determining abnormalsticking of the lock-up clutch in the engaged position, can be found,for example, in Patent Reference 1 (International Publication WO2014/017239). The teaching of Patent Reference 1 is to detect ordetermine engage-position sticking of a lock-up clutch based on a torqueconverter slip ratio of transmission input rotational speed relative toprime mover (e.g., internal combustion engine) output rotational speed,and hydraulic oil temperature.

SUMMARY OF THE INVENTION

A lock-up clutch is engaged when an automatic transmission assumes apredetermined (speed) gear, thereby improving the efficiency of powertransmission from a prime mover to the automatic transmission andenhancing fuel economy performance. However, if the lock-up clutch isaccidentally engaged when the automatic transmission is not in thepredetermined gear, risks arise including shock caused by prime moverrotational speed fluctuation being transmitted to the transmission andof stalling occurring when the gear is changed during vehicledeceleration.

In light of this, the teaching of Patent Reference 1 is to detect ordetermine that the lock-up clutch is stuck in the engaged position when,in the absence of a lock-up clutch engage command, the calculated torqueconverter slip ratio is small and the temperature of the hydraulic oilis low. However, depending on the vehicle driving environment, ambienttemperature and other factors, the calculated slip ratio may beabnormally small even in the absence of a lock-up clutch engage command,and in such a case, a false lock-up clutch engage-position stickingdetermination may make it difficult to implement fail-safe controlappropriately.

The object of this invention is therefore to overcome the aforesaidproblem by providing a control apparatus for an automatic transmissionthat can reliably determine or detect lock-up clutch engage-positionsticking and implement appropriate fail-safe control.

In order to achieve the object, this invention provides an apparatus forcontrolling an automatic transmission that is connected to a prime movermounted on a vehicle and changes speed of rotation of the prime mover totransmit the speed of rotation to driven wheels, having a torqueconverter interposed between the prime mover and the automatictransmission and equipped with a lock-up clutch, a hydraulic supplycircuit that supplies hydraulic pressure to the lock-up clutch and theautomatic transmission, and a controller that controls operation of thelock-up clutch and the automatic transmission through the hydraulicsupply circuit, comprising: a rotational speed ratio calculator thatcalculates a ratio of an input rotational speed of the automatictransmission relative to an output rotational speed of the prime mover;and a lock-up clutch engage-position sticking determiner that causes thecontroller to form a lock-up clutch engaging circuit through thehydraulic supply circuit when it is determined that predeterminedoperating conditions of the vehicle are satisfied at vehicle drive-off,determines whether engage-position sticking malfunction of the lock-upclutch has occurred based on the calculated ratio and a change rate ofthe output rotational speed of the prime mover when the lock-up clutchengaging circuit has been formed, and causing the controller toimplement fail-safe control when the sticking is determined.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages will be more apparent fromthe following description and drawings in which:

FIG. 1 is an overall schematic view of a control apparatus for anautomatic transmission according to an embodiment of this invention;

FIG. 2 is a hydraulic circuit diagram concretely illustrating part ofthe structure of the hydraulic pressure supply circuit shown in FIG. 1;

FIGS. 3A and 3B are a set of hydraulic circuit diagrams explainingoperation of the hydraulic pressure supply circuit shown in FIG. 2;

FIG. 4 is a flowchart showing operation of the apparatus according tothe embodiment of this invention;

FIG. 5 is a time chart explaining processing of the flowchart of FIG. 4;and

FIG. 6 is a time chart similarly explaining processing of the flowchartof FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

A control apparatus for an automatic transmission according to anembodiment of this invention will be explained with reference to theattached drawings in the following.

FIG. 1 is an overall schematic view of a control apparatus for anautomatic transmission according to an embodiment of this invention.

Reference numeral 1 in FIG. 1 designates a vehicle equipped with anautomatic transmission (called “transmission” hereinafter) T. Thetransmission T is a twin-clutch (double-clutch) transmission with 8forward-speed and 1 reverse-speed gears and has P, R, N and D ranges,for example.

The transmission T is connected through a torque converter 12 to adriveshaft 10 a connected to a crankshaft of an engine (prime mover) 10,and is equipped with an even-numbered speed (2, 4, 6 and 8 speed) inputshaft (second input shaft) 14 and with an odd-numbered speed (1, 3, 5and 7 speed) input shaft (first input shaft) 16 parallel to theeven-numbered speed input shaft 14. The engine 10 is, for example, agasoline-fueled, spark-ignition internal combustion engine.

The torque converter 12 has a pump impeller 12 b fixed on a drive plate12 a directly connected to the driveshaft 10 a of the engine 10, aturbine runner 12 c fixed on the even-numbered speed input shaft 14, anda lock-up clutch 12 d, whereby the driving force (rotation) of theengine 10 is inputted to the even-numbered speed input shaft 14 throughthe torque converter 12.

An idler shaft 18 is provided in the transmission T in parallel with theeven-numbered speed input shaft 14 and odd-numbered speed input shaft16. The even-numbered speed input shaft 14 is connected to the idlershaft 18 through gears 14 a, 18 a, and the odd-numbered speed inputshaft 16 is connected to the idler shaft 18 through gears 16 a, 18 a,whereby the even-numbered speed input shaft 14, the odd-numbered speedinput shaft 16, and idler shaft 18 rotate together with the rotation ofthe engine 10.

Further, a first auxiliary input shaft 20 and a second auxiliary inputshaft 22 are concentrically installed on the peripheries of theodd-numbered speed input shaft 16 and the even-numbered speed inputshaft 14 respectively to be rotatable relative thereto.

The odd-numbered speed input shaft 16 and first auxiliary input shaft 20are connected through a first clutch 24 and transmit rotation of theengine 10 through the first clutch 24, while the even-numbered speedinput shaft 14 and the second auxiliary input shaft 22 are connectedthrough a second clutch 26 and transmit rotation of the engine 10through the second clutch 26. The first and second clutches 24 and 26comprise of wet multi-plate clutches that operate by being supplied withworking oil pressure (hydraulic pressure).

An output shaft 28 is installed between and in parallel with theeven-numbered speed input shaft 14 and odd-numbered speed input shaft16. The even-numbered speed input shaft 14, odd-numbered speed inputshaft 16, idler shaft 18 and output shaft 28 are rotatably supported bybearings 30.

On the first auxiliary input shaft 20 on the odd-numbered speed side arefixed a first-speed drive gear 32, a third-speed drive gear 34, afifth-speed drive gear 36 and a seventh-speed drive gear 38, and on thesecond auxiliary input shaft 22 on the even-numbered speed side arefixed a second-speed drive gear 40, a fourth-speed drive gear 42, asixth-speed drive gear 44 and an eighth-speed drive gear 46.

On the output shaft 28 are fixed a first-second speed driven gear 48that mates with the first-speed drive gear 32 and the second-speed drivegear 40, a third-fourth speed driven gear 50 that mates with thethird-speed drive gear 34 and the fourth-speed drive gear 42, afifth-sixth speed driven gear 52 that mates with the fifth-speed drivegear 36 and the sixth-speed drive gear 44, and a seventh-eighth speeddriven gear 54 that mates with the seventh-speed drive gear 38 andeighth-speed drive gear 46.

The idler shaft 18 rotatably supports an RVS (reverse) idler gear 56that mates with the first-second speed driven gear 48 fixed on theoutput shaft 28. The idler shaft 18 and the RVS idler gear 56 areconnected through an RVS clutch 58. Like the first and second clutches24 and 26, the RVS clutch 58 also comprises a wet multi-plate clutchthat operates by being supplied with hydraulic pressure.

On the odd-numbered speed input shaft 16 are provided a first-thirdspeed gear engaging mechanism 60(1-3) that selectively engages or fixesthe first-speed drive gear 32 and the third-speed drive gear 34 with thefirst auxiliary input shaft 20, and a fifth-seventh speed gear engagingmechanism 60(5-7) that selectively engages or fixes the fifth-speeddrive gear 36 and the seventh-speed drive gear 38 with the firstauxiliary input shaft 20.

On the even-numbered speed input shaft 14 are provided a second-fourthspeed gear engaging mechanism 60(2-4) that selectively engages or fixesthe second-speed drive gear 40 and the fourth-speed drive gear 42 withthe second auxiliary input shaft 22, and a sixth-eighth speed gearengaging mechanism 60(6-8) that selectively engages or fixes thesixth-speed drive gear 44 and the eighth-speed drive gear 46 with thesecond auxiliary input shaft 22. The four gear engaging mechanisms aredesignated collectively by reference symbol 60.

When the first clutch 24 or the second clutch 26 is engaged, the drivingforce of the engine 10 is transmitted from the odd-numbered speed inputshaft 16 to the first auxiliary input shaft 20 or from the even-numberedspeed input shaft 14 to the second auxiliary input shaft 22 and furtherto the output shaft 28 through the aforesaid drive gears and drivengears.

During reverse operation, the driving force of the engine 10 istransmitted to the output shaft 28 through the even-numbered speed inputshaft 14, gear 14 a, gear 18 a, idler shaft 18, RVS clutch 58, RVS idlergear 56, and first-second speed driven gear 48. The output shaft 28 isconnected to a differential mechanism 64 through gears 28 a and 62, andthe differential mechanism 64 is connected to wheels (driven wheels) 68through drive shafts 66. The vehicle 1 is represented by wheels 68 andother components.

All of the gear engaging mechanisms 60 are operated by being suppliedwith hydraulic pressure (indicative of shifting force). A hydraulicpressure supply circuit 70 is provided for supplying hydraulic pressureto the gear engaging mechanisms 60, first and second clutches 24 and 26,RVS clutch 58 and torque converter 12.

FIG. 2 is a hydraulic circuit diagram concretely illustrating part ofthe structure of the hydraulic pressure supply circuit 70, withparticular focus on the portions related to control of the lock-upclutch 12 d. FIG. 2 shows a state in which a circuit (lock-up clutchengaging circuit) has been formed that is capable of supplying engagingpressure to the lock-up clutch 12 d.

In the hydraulic pressure supply circuit 70, hydraulic oil pumped from areservoir by an oil pump is pressure-regulated to the required pressure(LC engaging pressure) by a regulator valve and a torque converterregulator valve (neither shown) and supplied to an oil passage 70 a.

The LC engaging pressure supplied to the oil passage 70 a is sentthrough a branch passage 70 a 1 to an LC shift valve 70 b and is alsosupplied through an oil passage 70 c to an internal pressure chamber 12d 1 of the torque converter to press the lock-up clutch 12 d toward theengage-position (side of a backpressure chamber 12 d 2).

On the other hand, hydraulic pressure sent from the oil passage 70 athrough a branch passage 70 a 2 to an LC control valve 70 d is suitablypressure-regulated there and is then supplied through an oil passage 70e, the LC shift valve 70 b and an oil passage 70 f to a backpressurechamber 12 d 2 to press the lock-up clutch 12 d toward thedisengage-position (side of the internal pressure chamber 12 d 1).

The LC control valve 70 d houses a spool and its position(pressure-regulation point) changes in response to hydraulic pressure(LC control pressure) sent from a linear solenoid valve (electromagneticcontrol valve) 70 g through an oil passage 70 h. More specifically, theposition of the spool of the LC control valve 70 d can be varied bycontrolling current flow supplied to the linear solenoid valve 70 g soas to regulate the LC control pressure. With this, the hydraulicpressure inputted to the LC control valve 70 d through the branchpassage 70 a 2 can be suitably regulated for output to the backpressurechamber 12 d 2 of the torque converter 12. Therefore, the engagingforce, i.e., the slip ratio of the lock-up clutch 12 d is controlled byregulating the hydraulic pressure difference between the LC engagingpressure supplied to the internal pressure chamber 12 d 1 and thehydraulic pressure supplied to the backpressure chamber 12 d 2.

The linear solenoid valve 70 g is a hydraulic control valve configuredas an N/C (normally closed) valve that moves the spool in proportion toapplied current flow so as to vary or regulate pressure output from itsoutput port in accordance with a linear characteristic, and when nocurrent is applied, moves the spool to the closed position.

Some of the hydraulic oil supplied to the internal pressure chamber 12 d1 of the torque converter 12 is discharged through an oil passage 70 ito moving parts of the automatic transmission as lubricating oil.

The operation of the LC shift valve 70 b is controlled by on-offsolenoid valves 70 j and 70 k. This embodiment is configured so thatwhen the on-off solenoid valves 70 j and 70 k are both de-energized, theposition of a spool of the LC shift valve 70 b is that indicated in FIG.2, by which the aforesaid lock-up clutch engaging circuit is formed andthe hydraulic pressure is supplied both to the internal pressure chamber12 dl and to the backpressure chamber 12 d 2.

On the other hand, when either or both of the on-off solenoid valves 70j and 70 k are energized, the position of the spool of the LC shiftvalve 70 b moves to the left side in the figure to form a circuit thatdoes not supply hydraulic pressure or cuts off supply of hydraulicpressure to the internal pressure chamber 12 dl of the lock-up clutch 12d.

More specifically, when either or both of the on-off solenoid valves 70j and 70 k are energized to move the spool position of the LC shiftvalve 70 b to the left side in the figure, the branch passage 70 al andthe oil passage 70 f communicate, while the oil passage 70 e is cut offby the LC shift valve 70 b. Further, the oil passage 70 c connected tothe internal pressure chamber 12 d 1 is communicated with the oilpassage 70 l, so that the hydraulic pressure that has been supplied tothe internal pressure chamber 12 dl is discharged. Thus, in this state,hydraulic pressure is supplied to only the backpressure chamber 12 d 2and the lock-up clutch 12 d is disengaged.

Based on the foregoing, explanation will be made with reference to FIG.3A and FIG. 3B regarding occurrence of abnormal sticking of the lock-upclutch 12 d in the engage-position, more exactly occurrence of amalfunction in the linear solenoid valve 70 g that controls theoperation of the lock-up clutch 12 d.

FIGS. 3A and 3B are a set of figures that show a state in which theamount of current (lock-up clutch control pressure command value) sentto the LC control valve 70 d is zero, i.e., in the absence of a commandto engage the lock-up clutch 12 d, wherein FIG. 3A shows a case in whichthe linear solenoid valve 70 g is operating normally and FIG. 3B shows acase in which a malfunction has occurred in the linear solenoid valve 70g, specifically a malfunction that causes the linear solenoid valve 70 gto be stuck to a valve opening position by being undesirably suppliedwith high current or by spool's foreign particle biting, etc. Both ofFIGS. 3A and 3B show a state in which the lock-up clutch engagingcircuit has been formed, i.e., a state in which both of the on-offsolenoid valves 70 j and 70 k are de-energized.

As shown in FIG. 3A, in a case where the linear solenoid valve 70 g isoperating normally and the lock-up clutch control pressure command valueis zero, the valve position of the LC control valve 70 d is in theinitial state (closed position). In this case, the LC engaging pressureinput to the LC control valve 70 d is outputted from the LC controlvalve 70 d and supplied to the backpressure chamber 12 d 2 through theoil passage 70 e, LC shift valve 70 b and oil passage 70 f without beingregulated or lowered. Simultaneously, the LC engaging pressure is alsosupplied to the internal pressure chamber 12 dl through the branchpassage 70 a 1, LC shift valve 70 b and oil passage 70 c.

In other words, the internal pressure chamber 12 dl and the backpressurechamber 12 d 2 of the torque converter 12 are supplied with equalhydraulic pressures, so that the lock-up clutch 12 d is maintained at aneutral position in a disengaged state (zero LC capacity state).

However, as shown in FIG. 3B, when the malfunction to stick the linearsolenoid valve 70 g in the opening position occurs, the spool of the LCcontrol valve 70 d is forcibly moved to the left side in the figure, sothat the circuit connecting the branch passage 70 a 2 and the oilpassage 70 e is cut off by the LC control valve 70 d. Further, thehydraulic oil that has been supplied to the backpressure chamber 12 d 2is discharged to the reservoir through the oil passages 70 f and 70 e.As a result, the lock-up clutch 12 d is engaged and LC capacity isgenerated, and in the particular state shown in FIG. 3B, the lock-upclutch 12 d assumes a completely engaged condition.

Although the hydraulic pressure supply circuit 70 plays a role insupplying hydraulic oil not only to the torque converter 12 but also tothe gear engaging mechanisms 60, first and second clutches 24 and 26,and RVS clutch 58 of the transmission T, explanation with regard tothese constituents is omitted because they are not directly related tothe present invention.

Returning to the explanation of FIG. 1, the transmission T is equippedwith a shift controller 74. The shift controller 74 comprises anelectronic control unit (ECU) equipped with a microcomputer. Further, anengine controller 76, similarly comprising an electronic control unit(ECU) equipped with a microcomputer, is installed for controllingoperation of the engine 10.

The shift controller 74 is configured to communicate with the enginecontroller 76 and acquires various information from the enginecontroller 76, including engine speed (output rotational speed of theprime mover) NE, throttle opening, and accelerator position AP.

First, second, third and fourth rotational speed sensors 82, 84, 86 and90 installed on the transmission T respectively output a signalindicating input rotational speed NM of the transmission T, signalsindicating rotational speeds of the first and second auxiliary inputshafts 20, 22, and a signal indicating rotational speed of the outputshaft 28 (output rotational speed of the transmission T) NC (namely,vehicle speed V).

First and second hydraulic pressure sensors 94 and 96 provided on oilpassages of the hydraulic pressure supply circuit 70 connected to thefirst and second clutches 24 and 26 output signals indicating hydraulicoil pressures supplied to the first and second clutches 24 and 26.

A range selector position sensor 102 provided near a range selector (notshown) installed at a driver's seat of the vehicle 1 outputs a signalindicating a range to which the driver has operated the range selector(selected range) among, for example, P, R, N and D ranges.

The outputs of these sensors are all sent to the shift controller 74.Based on these sensor outputs, plus other data obtained throughcommunication with the engine controller 76, the shift controller 74energizes/de-energizes linear solenoid valves and the like (none ofwhich are shown) to control the operation of the first and secondclutches 24 and 26, RVS clutch 58, gear engaging mechanisms 60 andlock-up clutch 12 d, and thereby control the operation of thetransmission T. In this specification, the shift controller 74constitutes the control apparatus for the automatic transmission.

The operation of the apparatus of this embodiment will be explainednext. As explained in the foregoing, the object of this embodiment is toreliably determine or detect at the time of vehicle 1 drive-off (start)whether the lock-up clutch 12 d has incurred engage-position stickingmalfunction, i.e., whether energization of the linear solenoid valve 70g, spool's foreign particle biting and the like has occurred, so as toenable appropriate implementation of fail-safe control.

FIG. 4 is a flowchart showing this control. The process according tothis flowchart is initiated once when the vehicle 1 drives off.

Now to explain, the program begins at S10, in which it is determinedwhether predetermined operating conditions of the vehicle 1 that enablesimplementation of engage-position sticking discrimination/control of thelock-up clutch 12 d are satisfied at vehicle drive-off (S: processStep).

By “predetermined operating conditions” are specifically meant toinclude one or more that the engine 10 is running (IG turned ON), thatthe voltage of a battery (not shown) constituting the power source ofthe shift controller 74 is equal to or greater than a predeterminedvalue that ensures operation of the shift controller 74, that the outputrotational speed NE of the engine 10 is equal to or greater than apredetermined rotational speed, that the input rotational speed NM ofthe transmission T is equal to or greater than a prescribed rotationalspeed, that fuel-cut control of the engine 10 is not in effect, that thegear of the transmission T is set to the first-speed gear (LOW), thatthe lock-up clutch control pressure command value (current flow throughthe linear solenoid valve 70 g) that determines the engaging pressure ofthe lock-up clutch 12 d is less than a predetermined value, that theamount of accelerator position AP change is not negative, that enginetorque is equal to or greater than a predetermined torque, that this isthe first malfunction discrimination processing performed in the currentdriving cycle (one cycle from IG turned ON to IG turned OFF), and thatthe ratio of the input rotational speed NM of the transmission Trelative to the output speed NE of the engine 10 (NM/NE; indicated asETR in FIG. 4 and other drawings) is equal to or less than apredetermined ratio (second predetermined ratio).

These conditions will be explained in detail. As explained withreference to FIG. 2, the hydraulic pressure supplied to the hydraulicpressure supply circuit 70 is generated by an oil pump driven by theengine 10. Therefore, no hydraulic pressure is generated in thehydraulic pressure supply circuit 70 unless the engine 10 is running.For this reason, that the engine 10 is running (IG turned ON) is made acondition.

Accurate malfunction detection control cannot be performed when theshift controller 74 that performs the control shown in FIG. 4 is itselfnot being supplied with adequate power. Therefore, that the voltage ofthe power supply (battery) is equal to or greater than a predeterminedvalue is made a condition.

Depending on the accuracy of the rotational speed sensor 82, a riskarises of not being possible to accurately detect rotational speed whenthe output speed NE of the engine 10 or the transmission inputrotational speed NM is extremely low. Therefore, that the output enginespeed NE is equal to or greater than a predetermined rotational speedand the transmission input rotational speed NM is equal to or greaterthan a prescribed rotational speed is made a condition. Further, inorder to enable accurate malfunction detection, the engine 10 isconfirmed not to be in an unstable rotating condition by setting asadditional conditions that fuel-cut control of the engine 10 is not ineffect, that the amount of accelerator position AP change is notnegative, and that engine torque is not less than a predeterminedtorque.

In view of the fact that the control in this embodiment is implementedat drive-off of the vehicle 1 in an operating region in which thelock-up clutch 12 d is not ordinarily engaged, that the gear of thetransmission T is set to first-speed gear (LOW) is made a condition.Further, when the lock-up clutch control pressure command value thatdetermines the engaging pressure of the lock-up clutch 12 d is equal toor greater than a predetermined pressure, more exactly in a situationwhere the lock-up clutch control pressure command value is not set tozero and LC control pressure can be produced irrespective of abnormalityof the linear solenoid valve 70 g, a false determination ofengage-position sticking malfunction might occur. Therefore, that thelock-up clutch control pressure command value is less than apredetermined value is made a condition.

Moreover, in order to avoid false determination, the processing isperformed only once at drive-off of the vehicle 1. Therefore, that thisis the first malfunction discrimination processing performed in thecurrent driving cycle is made a condition.

In addition, discrimination is commenced from an unmistakably disengagedstate of the lock-up clutch 12 d and to ensure reliable discriminationof engage-position sticking malfunction of the lock-up clutch 12 d, thatETR at the start of control is equal to or less than the secondpredetermined ratio, i.e., that the differential rotation between theengine speed NE and the transmission input rotational speed NM is largeis made a condition.

In the flowchart, when the result in S10 is NO, engage-position stickingmalfunction of the lock-up clutch 12 d cannot be accurately determined,so the program is terminated without performing the processing explainedbelow. On the other hand, when the result in S10 is YES, the programproceeds to S12, in which the solenoid valves 70 j and 70 k are bothde-energized to form the lock-up clutch engaging circuit (indicated as“LC ON circuit” in FIG. 4).

At drive-off of the vehicle 1, ordinarily the lock-up clutch 12 d isdisengaged and control is performed to amplify the torque of the engine10 through the torque converter 12. In a normal situation, therefore, nolock-up clutch engaging circuit is formed at drive-off of the vehicle 1.

However, as explained with reference to FIG. 2, when no lock-up clutchengaging circuit is formed, hydraulic pressure is not supplied to theinternal pressure chamber 12 d 1 of the lock-up clutch 12 d, so thateven if abnormality should occur in the linear solenoid valve 70 g thatcontrols the operation of the lock-up clutch 12 d, engage-positionsticking malfunction of the lock-up clutch 12 d cannot be determined ordetected. So in this embodiment, the lock-up clutch engaging circuit isintentionally formed (S12) when it is determined in S10 that thepredetermined operating conditions of the vehicle 1 are satisfied.

The program next proceeds to S14, in which it is determined whether thevalue of a timer for preventing false detection (false detectionprevention timer) has reached zero, i.e., it is determined whether atime period has passed. The false detection prevention timer is acountdown timer provided for determining whether the engine 10 hasreached a stable condition (so-called steady-state condition) after thevehicle 1 satisfied the predetermined operating conditions when itdrives off. A configuration is also possible that determinesestablishment of the predetermined operating conditions, including theforming of the lock-up clutch engaging circuit in S12 and the passage ofthe false detection prevention timer time period in S14.

So long as the result in S14 remains NO, there is a risk of the rotationof the engine 10 being unstable, so the processing discussed later isskipped and the aforesaid processing is repeated until the result in S14becomes YES. When the result in S14 is YES, the program proceeds to S16,in which it is determined whether the slip ratio (ETR) of the inputrotational speed NM of the transmission T relative to the output speedNE of the engine 10, i.e., NM/NE is equal to or greater than apredetermined ratio. Here, the slip ratio (ETR) means the torqueconverter speed ratio.

The predetermined ratio is set to a value by which it can be determinedthat the differential rotation between the engine speed NE and the inputrotational speed NM of the transmission is small and the lock-up clutch12 d is almost fully or fully engaged, namely to around 1.0. Therefore,when the result in S16 is NO, the program proceeds to S18, in which itis determined that no engage-position sticking malfunction of thelock-up clutch 12 d has occurred.

On the other hand, when the result in S16 is YES, the program proceedsto S20, in which it is determined whether change in engine speed NE perunit time (change rate) ΔNE at the time of the first affirmative resultin S16, i.e., at the time point of the first determination of thecalculated ETR being equal to or greater than the predetermined ratio,is negative.

As stated above, at drive-off of the vehicle 1, the lock-up clutchengaging circuit is not formed until the result in S10 becomes YES, andsince the rotation of the engine 10 is inputted to the transmission Tthrough the torque converter 12 in the embodiment, the engine speed NEand the transmission input rotational speed NM are ordinarily differentat this time point, with the engine speed NE being somewhat higher thanthe transmission input rotational speed NM.

However, when a malfunction occurs in the linear solenoid valve 70 gthat controls the lock-up clutch 12 d, then upon formation of thelock-up clutch engaging circuit, the lock-up clutch 12 d is forciblyengaged even if the lock-up clutch control pressure command value is notgenerated and zero, whereupon the engine speed NE and the transmissioninput rotational speed NM converge on substantially the same value,namely, a phenomenon arises of the engine speed NE decelerating underthe influence of the input rotational speed NM.

As was stated concerning the object of the present invention, dependingon the driving environment, ambient temperature and the like of thevehicle 1, the output engine speed NE and the transmission inputrotational speed NM sometimes become substantially the same (i.e., ETRbecomes equal to or greater than the predetermined ratio) even when noengage-position sticking has occurred in the lock-up clutch 12 d.However, in the case where engage-position sticking malfunction of thelock-up clutch 12 d has not occurred, no phenomenon occurs of the enginespeed NE decelerating despite the operation of the engine 10 beingstable.

In this embodiment, therefore, accurate detection or determination ofengage-position sticking malfunction of the lock-up clutch 12 d is madepossible by making a determination in S20 as to whether the engine speedNE change rate ΔNE is negative.

In the flowchart, when the result in S20 is NO, the program proceeds toS18, in which engage-position sticking malfunction of the lock-up clutch12 d is determined not to have occurred. When, to the contrary, theresult in S20 is YES, the program proceeds to S22, in which it isdetermined whether the value of an NG counter is equal to or greaterthan a threshold value.

The NG counter counts the time period during which ETR is continuouslyequal to or greater than the predetermined ratio and is set to aninitial value of zero. The first result in S22 is therefore NO, and theprogram proceeds to S24, in which the value of the NG counter isincremented by 1, whereafter the foregoing processing is repeated untilthe determination in S22 becomes YES. It should be noted that thedetermination in the aforesaid S20 needs to be made only at the time ofthe first affirmative determination in S16 and can therefore be skippedin the second and ensuing determinations.

The threshold value is set to a value that makes it possible todetermine that engage-position sticking malfunction of the lock-upclutch 12 d has unmistakably occurred, and in this specification thetime period defined by the threshold value is called a prescribed timeperiod. Up to the time that the determination in S22 becomes YES, thevalue of the NG counter is reset to zero when the determination in anyof S10, S14 and S116 is negative.

When the result in S22 is YES, i.e., when ETR is determined to have beenequal to or greater than the predetermined ratio continuously for theprescribed time period or longer (i.e., when it is determined that ETRis kept to be equal to or greater than the predetermined ratio for theprescribed time period or longer), the program proceeds to S26, in whichit is determined that engage-position sticking malfunction of thelock-up clutch 12 d has occurred.

The program next proceeds to S28, in which fail-safe control (Fail-SafeAction) is implemented. Specifically, a warning device or indicatorinstalled on the dashboard at the driver's seat is used to caution thedriver, and engine stall-avoidance control is implemented to disengageall of the clutches connecting the engine 10 and the wheels 68 (firstand second clutches 24, 26 and RVS clutch 58), whereafter the program isterminated.

The reason for this is that the engine might stall if the vehicle 1 wereto be decelerated and stopped with the lock-up clutch 12 d havingsustained engage-position sticking malfunction. So in this embodiment,when the lock-up clutch 12 d is determined to have sustainedengage-position sticking, the clutches 24, 26 and 58 that transmit theoutput of the engine 10 to the wheels 68 are all disengaged to preventtransmission of torque to the engine 10 from the side of the wheels 68,thereby reliably avoiding stalling of the engine.

FIGS. 5 and 6 are time charts for explaining the aforesaid operations.

To explain first with reference to FIG. 5, when the predeterminedoperating conditions are established at time t1, the solenoid valves 70j and 70 k are de-energized to form the lock-up clutch engaging circuit(LC ON circuit) and the false detection prevention timer counting isstarted. When the timer count becomes zero at time t2, determination ofwhether the slip ratio (ETR) of the transmission input rotational speedNM relative to the engine output speed NE (NM/NE) is equal to or greaterthan the predetermined ratio is commenced.

Upon the first determination of the slip ratio (ETR) having become equalto or greater than the predetermined ratio at time t3, a determinationis made as to whether the engine speed NE change rate ΔNE at this timeis negative. Since, as illustrated, the value of ΔNE at time t3 isnegative, the value of the NG counter for determining engage-positionsticking malfunction of the lock-up clutch 12 d is successivelyincremented.

When the value of the NG counter becomes equal to or greater than thethreshold value at time t4, occurrence of engage-position stickingmalfunction of the lock-up clutch 12 d, namely occurrence of abnormalitysuch as unintentional energization in the linear solenoid valve 70 gthat controls operation of the lock-up clutch 12 d, is determined,whereupon the bit of an LC engage-position sticking NG flag is set to 1and fail-safe control of the vehicle 1 is started.

On the other hand, as shown in FIG. 6, when the lock-up clutch 12 d hasnot sustained engage-position sticking malfunction, then even after thecount of the false detection prevention timer becomes zero at time t2and up to the implementation of shift control at time t5, neither doesthe slip ratio (ETR) become equal to or greater than the predeterminedratio nor is there a determination of engage-position stickingmalfunction of the lock-up clutch 12 d having occurred.

As stated above, the embodiment is configured to have an apparatus ormethod for controlling an automatic transmission (T) that is connectedto a prime mover (engine 10) mounted on a vehicle (1) and changes speedof rotation of the prime mover (10) to transmit the speed of rotation todriven wheels (68), having a torque converter (12) interposed betweenthe prime mover (10) and the automatic transmission (T) and equippedwith a lock-up clutch (12 d), a hydraulic supply circuit (70) thatsupplies hydraulic pressure to the lock-up clutch (12 d) and theautomatic transmission (T), and a controller (74) that controlsoperation of the lock-up clutch (12 d) and the automatic transmission(T) through the hydraulic supply circuit (70), comprising: a rotationalspeed ratio calculator (74) that calculates a ratio (ETR) of an inputrotational speed of the automatic transmission (T) relative to an outputrotational speed of the prime mover (12); and a lock-up clutchengage-position sticking determiner (74, S10-S28) that causes thecontroller to form a lock-up clutch engaging circuit through thehydraulic supply circuit (70) when it is determined that predeterminedoperating conditions of the vehicle (1) are satisfied at vehicledrive-off, determines whether engage-position sticking malfunction ofthe lock-up clutch (12 d) has occurred based on the calculated ratio(ETR) and a change rate (ΔNE) of the output rotational speed of theprime mover (12) when the lock-up clutch engaging circuit has beenformed, and causing the controller to implement fail-safe control whenthe sticking is determined. Therefore, occurrence of engage-positionsticking malfunction of the lock-up clutch 12 d can be accuratelydetermined at vehicle drive-off.

Particularly since engage-position sticking malfunction of the lock-upclutch 12 d is determined based on the prime mover output rotationalspeed change rate, occurrence of engage-position sticking malfunction ofthe lock-up clutch 12 d can be accurately determined, making it possibleto implement appropriate fail-safe control for avoiding shock occurrenceduring driving in a condition with the lock-up clutch 12 d stuck in theengaged position.

In the apparatus or method, the lock-up clutch engage-position stickingdeterminer determines that the engage-position sticking malfunction ofthe lock-up clutch has occurred, when it is determined that thecalculated ratio (ETR) is kept to be equal to or greater than apredetermined ratio for a prescribed time period and when the changerate (ΔNE) of the output rotational speed of the prime mover (10) wasnegative at a time at which the calculated ratio (ETR) was firstdetermined to be equal to or greater than the predetermined ratio(S10-S26), whereby, in addition to the aforesaid effects and advantages,it becomes possible to determine occurrence of engage-position stickingmalfunction of the lock-up clutch 12 d even more accurately.

In the apparatus or method, the lock-up clutch engage-position stickingdeterminer causes the controller to implement the fail-safe control bydisengaging clutches (first, second clutches 24, 26, RVS clutch 58) thattransmit the output of the prime mover to driven wheels when it isdetermined that the engage-position sticking malfunction of the lock-upclutch (12 d) has occurred (S28), whereby, in addition to the aforesaideffects and advantages, it becomes possible to avoid shock occurrenceduring driving in a condition with the lock-up clutch 12 d stuck in theengaged position and to implement fail-safe control for preventingstalling of the prime mover even more appropriately.

In the apparatus or method, the predetermined operating conditionsinclude at least that the output rotational speed of the prime mover(10) is equal to or greater than a predetermined rotational speed, thatthe input rotational speed of the automatic transmission (T) is equal toor greater than a prescribed rotational speed, that the calculated ratio(ETR) is equal to or less than a second predetermined ratio, and that alock-up clutch control pressure command value that defines engagingpressure of the lock-up clutch (12 d) is less than a predeterminedvalue, whereby, in addition to the aforesaid effects and advantages,occurrence of a false lock-up clutch engage-position stickingdetermination can be appropriately avoided and occurrence ofengage-position malfunction of the lock-up clutch 12 d can be even moreaccurately determined.

In the apparatus or method, the predetermined conditions include thatthe prime mover (10) is under a stable rotating condition, whereby, inaddition to the aforesaid effects and advantages, occurrence of a falselock-up clutch engage-position sticking determination can be moreappropriately avoided.

In the apparatus or method, the predetermined conditions include that agear of the automatic transmission (T) is set to a gear (e.g., firstspeed gear) to be used at the vehicle drive-off, whereby, in addition tothe aforesaid effects and advantages, occurrence of a false lock-upclutch engage-position sticking determination can be more appropriatelyavoided.

In the apparatus or method, wherein the lock-up clutch engage-positionsticking determiner determines the engage-position sticking malfunctionof the lock-up clutch (12 d) only once at the vehicle drive-off,whereby, in addition to the aforesaid effects and advantages, thedetermination can be reduced to a necessary limit.

Although malfunction is determined using the slip ratio (ETR) of thetransmission input rotational speed NM relative to the engine outputspeed NE (NM/NE) in the aforesaid embodiment, it is possible instead tomake the determination based on its reciprocal (NE/NM) or based on thedifferential rotation between the transmission input rotational speed NMand the engine speed NE.

Further, the structure of the transmission T is not limited to theillustrated structure and any structure is acceptable insofar as it isprovided with a configuration similar to the aforesaid hydraulic supplycircuit.

Moreover, although various conditions are enumerated as thepredetermined operating conditions, the conditions are not necessarilylimited to these and, for example, conditions such as the temperature ofthe hydraulic oil can also be included.

Further, although an engine was exemplified as the prime mover, this isnot a limitation and, for example, the prime mover can instead by ahybrid of an engine and an electric motor.

While the invention has thus been shown and described with reference tospecific embodiment, it should be noted that the invention is in no waylimited to the details of the described arrangement; changes andmodifications may be made without departing from the scope of theappended claims.

What is claimed is:
 1. An apparatus for controlling an automatictransmission that is connected to a prime mover mounted on a vehicle andchanges speed of rotation of the prime mover to transmit the speed ofrotation to driven wheels, having a torque converter interposed betweenthe prime mover and the automatic transmission and equipped with alock-up clutch, a hydraulic supply circuit that supplies hydraulicpressure to the lock-up clutch and the automatic transmission, and acontroller that controls operation of the lock-up clutch and theautomatic transmission through the hydraulic supply circuit, comprising:a rotational speed ratio calculator that calculates a ratio of an inputrotational speed of the automatic transmission relative to an outputrotational speed of the prime mover; and a lock-up clutchengage-position sticking determiner that causes the controller to form alock-up clutch engaging circuit through the hydraulic supply circuitwhen it is determined that predetermined operating conditions of thevehicle are satisfied at vehicle drive-off, determines whetherengage-position sticking malfunction of the lock-up clutch has occurredbased on the calculated ratio and a change rate of the output rotationalspeed of the prime mover when the lock-up clutch engaging circuit hasbeen formed, and causing the controller to implement fail-safe controlwhen the sticking is determined.
 2. The apparatus according to claim 1,wherein the lock-up clutch engage-position sticking determinerdetermines that the engage-position sticking malfunction of the lock-upclutch has occurred, when it is determined that the calculated ratio iskept to be equal to or greater than a predetermined ratio for aprescribed time period and when the change rate of the output rotationalspeed of the prime mover was negative at a time at which the calculatedratio was first determined to be equal to or greater than thepredetermined ratio.
 3. The apparatus according to claim 1, wherein thelock-up clutch engage-position sticking determiner causes the controllerto implement the fail-safe control by disengaging clutches that transmitthe output of the prime mover to driven wheels when it is determinedthat the engage-position sticking malfunction of the lock-up clutch hasoccurred.
 4. The apparatus according to claim 1, wherein thepredetermined operating conditions include at least that the outputrotational speed of the prime mover is equal to or greater than apredetermined rotational speed, that the input rotational speed of theautomatic transmission is equal to or greater than a prescribedrotational speed, that the calculated ratio is equal to or less than asecond predetermined ratio, and that a lock-up clutch control pressurecommand value that defines engaging pressure of the lock-up clutch isless than a predetermined value.
 5. The apparatus according to claim 1,wherein the predetermined conditions further include that the primemover is under a stable rotating condition.
 6. The apparatus accordingto claim 1, wherein the predetermined conditions further include that agear of the automatic transmission is set to a gear to be used at thevehicle drive-off.
 7. The apparatus according to claim 1, wherein thelock-up clutch engage-position sticking determiner determines theengage-position sticking malfunction of the lock-up clutch only once atthe vehicle drive-off.
 8. A vehicle comprising the apparatus of claim 1.9. A method for controlling an automatic transmission connected to aprime mover mounted on a vehicle through a torque converter, comprising:calculating a ratio of an input rotational speed of the automatictransmission relative to an output rotational speed of the prime mover,and forming a lock-up clutch engaging circuit through a hydraulic supplycircuit when predetermined operating conditions of the vehicle aresatisfied at vehicle drive-off, determining whether an engage-positionsticking malfunction of a lock-up clutch of the torque converter hasoccurred based on the calculated ratio and a change rate of the outputrotational speed of the prime mover when the lock-up clutch engagingcircuit has been formed, and implementing fail-safe control when theengage-position sticking malfunction is determined.
 10. The methodaccording to claim 9, wherein determining that the engage-positionsticking malfunction of the lock-up clutch has occurred comprisesdetermining that the calculated ratio is equal to or greater than apredetermined ratio for a prescribed time period and when the changerate of the output rotational speed of the prime mover is negative at atime at which the calculated ratio is first determined to be equal to orgreater than the predetermined ratio.
 11. The method according to claim9, wherein implementing the fail-safe control comprises disengagingclutches that transmit the output of the prime mover to driven wheelswhen the engage-position sticking malfunction of the lock-up clutchoccurs.
 12. The method according to claim 9, wherein the predeterminedoperating conditions include at least that the output rotational speedof the prime mover is equal to or greater than a predeterminedrotational speed, that the input rotational speed of the automatictransmission is equal to or greater than a prescribed rotational speed,that the calculated ratio is equal to or less than a secondpredetermined ratio, and that a lock-up clutch control pressure commandvalue that defines engaging pressure of the lock-up clutch is less thana predetermined value.
 13. The method according to claim 9, wherein thepredetermined conditions further include that the prime mover is under astable rotating condition.
 14. The method according to claim 9, whereinthe predetermined conditions further include that a gear of theautomatic transmission is set to a gear to be used at the vehicledrive-off.
 15. The method according to claim 9, wherein determining theengage-position sticking malfunction of the lock-up clutch is performedonly once at the vehicle drive-off.